(1) Field of the Invention
The present invention relates to an optical pickup device that favorably records and reproduces information on and from an optical disc that includes a plurality of recording layers and an optical disc apparatus loaded with the above optical pickup device.
(2) Description of the Related Art
Development of an optical disc that includes a plurality of recording layers (a multilayer disc) and an optical disc apparatus corresponding to the above disc is now being promoted in order to increase the storage capacity of the optical disc. Since light (stray light) reflected from recording layers other than a target layer is present in the multilayer disc, how a signal is recorded on the target layer and reproduced from the target layer with accuracy arises as a subject.
For example, in Japanese Patent Application Laid-Open No. 2006-344344 (FIG. 3 and FIG. 5), there is described a configuration that “an optical beam of P-polarized light which has been emitted from a light source unit 51 is reflected by an optical disc 15 and is incident upon a lens 61 as S-polarized light. Then, in both of quarter wave plates 62 and 63, an optical phase difference of a plus quarter wave is given to the optical beam which has been incident upon the plus X side of an optical axis and an optical phase difference of a minus quarter wave is given to the optical beam which has been incident upon the minus X side thereof. Thus, signal light that passes through the quarter wave plate 63 turns to S-polarized light and stray light turns to P-polarized light, and then only the signal light transmits through a polarization optical element 64”, by presenting that “a desired signal is acquired from the optical disc that includes a plurality of recording layers with accuracy” as a subject to be solved, as a technology relating to the above.
In addition, in Technical Report CPM 2005-149, October 2005, p. 33, published from the Institute of Electronics, Information and Communication Engineers, there is described a configuration that “a photodetector for tracking is disposed in a region with no other-layer stray light”, by presenting that “In recording/reproducing information on/from a dual layer disc, when other-layer stray light which is light reflected from layers other than a target layer is incident upon the photodetector, offset occurs in a TE signal. Thus, in an existing configuration that no countermeasure is taken to the other-layer stray light, the offset of the TE signal is increased in the dual layer disc as compared with that in a single layer disc and hence stable control is disturbed” as a subject to be solved. A configuration which is similar to the above is described in Japanese Patent Application Laid-Open No. 2004-281026 (FIG. 22, FIG. 24 and FIG. 25).